Method for making a seal ring

ABSTRACT

In the manufacture of a seal ring having a cut portion at one position on the circumference by injecting a molten molding material from a gate into a cavity of a forming die, the gate is provided at a position apart from the opposite position to the cut, portion of the seal ring. In the case of a seal ring with a weld portion, the weld portion is set away from the cut portion.

This is a divisional of application Ser. No. 08/691,815 filed Jul. 31,1996, now U.S. Pat. No. 5,865,443.

BACKGROUND OF THE INVENTION

The present invention generally relates to a seal ring, a method ofmanufacturing the same, and a forming die of the same and moreparticularly relates to a seal ring used for sealing a portion wherehydraulic control of automatic transmissions of AT motorcars and thelike is required, a method of manufacturing the same, and a forming dieof the same.

FIG. 1 shows a conventional seal ring having a cut portion 2 at oneplace on its circumference.

A conventional injection molding die for forming such a seal ring isshown in FIG. 2. A molten molding material is pressed under highpressure into a cavity 4a through a gate 3 of a forming die 4A and thenit is hardened by cooling or heating.

In this case, if the flow length of the molten molding material in thecavity 4a within the forming die is too long, it sometimes occurs thatthe molding material is not completely filled into the cavity 4a of theforming die. Also, it sometimes occurs that the molding material beginsto harden before it fully flows into the cavity 4a of the forming die.In such cases, the molding material is not fully filled in the die and,hence, a work of exactly the same form as the die cannot be produced.Such Phenomena are called "short in a moulding" and "sink mark".

Therefore, to make the flow length of the molding material within thecavity 4a of the forming die as small as possible, it was practiced toprovide the gate 3 at the portion opposite to the cut portion 12. Moreparticularly, the cut portion 12 and the gate 3 were located along thedirection of the diameter 4a' of the circular cavity 4a.

When the seal ring 1 is loaded in place, the cut portion 2 is widened toleft and right. At that time, a maximum strain is generated at theopposite portion 5 to the cut portion 2.

When the gate 3 is provided at the position opposite to (the other sideacross the diameter of) the mold cut portion 12 of the forming die 4A,the seal ring 1 produced by such an arrangement has a lower strength.The reason is that the portion corresponding to the gate 3, i.e., theportion-corresponding-to-gate 13, has somewhat lowered strength comparedwith other portions of the seal ring 1. As a result, in the case where amaterial exhibiting smaller elongation is used as the material for theseal ring 1, it tends to break when it is loaded in place because theopposite portion 5 to the cut portion 2 of the seal ring 1 coincideswith the portion-corresponding-to-gate 13.

Further, a seal ring 1 can be molded by the use of a forming die 4Bhaving no cut portion as shown in FIG. 3. In this case, the seal ring. 1is cut at the position corresponding to the gate 3 and thus the cutportion 2 is provided. Namely, the portion-corresponding-to-gate becomesthe cut portion. In the case of FIG. 3, the flows of the moldingmaterial divided into two directions through the cavity 4b at the gate 3form the so-called weld portion 14 at the position where they meet eachother Since the weld portion 14 does not provide a perfect bond, it hassomewhat lowered strength as compared with other portions. Therefore, ifa weld portion 14 is formed at the opposite portion 15 to the cutportion 2, the cut portion 2 is widened when the seal ring is loaded inplace, and the opposite portion 15 to the cut portion 2 comes to bedamaged, especally for a material exhibiting small elongation.

On the other hand, generally, seal rings are molded out of moldingmaterials with PEEK used as the base. PEEK is a resin being hard andhaving a high melting point Therefore, moldings formed of such aPEEK-based forming material are hard and brittle. It is difficult tomake a cut with a knife in a PEEK seal ring after it has been molded. Ifit is forcibly cut, there arises a possibility of breaking it

Therefore, PEEK seal rings are molded by injecting the molding materialinto the cavity 4b of a forming die 4A having a mold cut portion 12previously provided as shown in FIG. 2. Otherwise, PEEK seal rings aremolded by the use of a forming die 4C partly joined at the cut portion 2as shown in FIG. 4A and FIG. 4B, and the portion 2a enclosed with brokenlines is cut off by using a milling machine in a subsequent workingprocess.

Further, the PEEK-based forming material is less fluid at the time ofinjection. Therefore, troubles of short shot are liable to occur whenthe flow length is too long or the flow passage area is too small.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a seal ring improved inloadability by having its strength improved, a method of manufacturingthe seal ring, and a forming die for use in the manufacturing method ofthe seal ring.

In the present invention, improvements are made on the position of thegate through which a molding material is injected into the cavity of aforming die and the position of the cut portion in the seal ring.

In one preferred mode of the present invention, when a cut portion isprovided at one position on the circumference of the cavity of a formingdie, the opposite portion to the cut portion of the seal ring is setaway from the position corresponding to the gate of the forming die.More particularly, the cut portion and the portion-corresponding-to-gateare not located along the direction of a diameter of the seal ring.Thereby, at the time when the seal ring is loaded in place, stress isprevented from concentrating in the portion-corresponding-to-gate of theseal ring having inferior strength. As a result, the seal ring becomesless breakable when the cut portion is widened.

In another mode of the invention, when no cut portion is provided on thecircumference of the cavity of a forming die, the cut portion of theseal ring is formed apart from the positions of both the weld portionand the portion-corresponding-to-gate. For example, the opposite portionto the cut portion where stress concentrates when the cut portion of theseal ring is widened is placed away from the position of the gate.Thereby, at the time when the seal ring is loaded in place, stress isprevented from concentrating in the portion-corresponding-to-gate andthe weld portion which are inferior in strength. As a result, the sealring becomes less breakable even when the cut portion is widened.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be described with reference to thedrawings, in which:

FIG. 1 is a perspective view showing a conventional seal ring having onecut portion;

FIG. 2 is a diagram schematically showing a structure of a forming diefor manufacturing the conventional seal ring shown in FIG. 1;

FIG. 3 is a diagram schematically showing a structure of a forming diefor manufacturing the conventional seal ring shown in FIG. 1;

FIG. 4A is a diagram schematically showing a structure of a forming diefor manufacturing a conventional seal ring;

FIG. 4B is an enlarged view showing the cut portion and its vicinity ofthe forming die of FIG. 4A;

FIG. 5 is a diagram schematically showing a structure of a forming diefor manufacturing a seal ring according to a preferred embodiment of theinvention;

FIG. 6 is a diagram schematically showing a structure of another formingdie for manufacturing a seal ring according to an embodiment of theinvention;

FIG. 7 is a diagram schematically showing a structure of a furtherforming die for manufacturing a seal ring according to an embodiment ofthe invention;

FIG. 8A is a front view showing a seal ring according to an embodimentof the invention;

FIG. 8B is a partially broken out side view of the seal ring shown inFIG. 8A;

FIG. 9 is a diagram showing the extended length of the cut portion ofthe seal ring shown in FIG. 8A;

FIG. 10 is a graph showing the relationship between the position of theportion-corresponding-to-gate relative to the cut portion (i.e., theangle between the cut portion and the portion-corresponding-to-gate) ofthe seal ring shown in FIG. 8A and the allowable extended length of thecut portion of the seal ring;

FIG. 11 is a diagram schematically showing a structure of a forming diefor manufacturing a seal ring according to another embodiment of theinvention;

FIG. 12A is a front view showing an example of seal rings manufacturedby the use of the forming die of FIG. 11;

FIG. 12B is a partially broken out side view of the seal ring shown inFIG. 12A; and

FIG. 13 is a graph showing the relationship between the position of theportion-corresponding-to-gate relative to the cut portion (i.e., theangle between the cut portion and the portion-corresponding-to-gate) ofthe seal ring shown in FIG. 12A and the allowable extended length of thecut portion of the seal ring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, kinds of the molding materials are notparticularly limited. As representative ones of generally used moldingmaterials, that having polyether ether keton (hereinafter called PEEK)as its base and that having tetrafluoroethylene-perfluoroalkylvinylethercopolymer (hereinafter called PFA) as its base can be used. Thesematerials are selected in terms of properties to be considered when theposition of the portion-corresponding-to-gate of the seal ring isdetermined.

EXAMPLE 1

Example 1 of the invention is an example for molding a seal ring out ofa PEEK-based molding-material.

PEEK is a resin being hard and having a high melting point Seal ringmoldings formed of the PEEK-based material is hard and brittle.

The PEEK-based molding material is less fluid when injected into a dieand, therefore, troubles of short shot are liable to occur when the flowlength is too long or the flow passage area is too small.

Although, in Example 1 of the invention, a seal ring is molded out ofthe PEEK-based material, such drawbacks with the use of the PEEK-basedmaterial are removed.

First, a manufacturing method of a seal ring of such a small diameter as30 mm or so in outer diameter will be described.

As shown in FIG. 5, the cavity 4d of a forming die 4D for manufacturingsuch a small-diametered seal ring has a relatively short flow length.Therefore, it is possible to mold the seal ring by the use of a formingdie 4D in which the gate 3 is provided adjacent to the mold cut portion12 of the forming die 4D. In this case, as apparent from FIG. 5, thegate 3 and the mold cut portion 12 are located extremely apart from theopposite position to them across the diameter of the circular cavity 4d.More particularly, the gate 3 is provided at a position far apart fromthe opposite portion 15 to the mold cut portion 12.

Now, a manufacturing method of a seal ring having an outer diameter of30 mm or more will be described.

The cavity 4e of a forming die 4E for manufacturing a seal ring of sucha large outer diameter has a long flow length. Therefore, it isdifficult to provide the gate 3 adjacent to mold the cut portion 12 asin the example shown in FIG. 5.

Therefore, in the cases of forming dies 4E and 4F, as shown in FIG. 6and FIG. 7, the gate 3 is provided at a position other than the portionadjacent to the cut portions 2 and 12 and the opposite portion 15 to themold cut portion 12. The gate 3 and the mold cut portions 2 and 12 areapart from the opposite positions thereto across the diameter of thecircular cavities 4e and 4f, and the gate 3 is provided at a positionapart from the opposite portion 15 to the cut portions 2 and 12.

In the case of the forming die 4E shown in FIG. 6, the outer diameter ofthe cavity 4e is 30-100 mm and the gate 3 is located at an angle ofapproximately 90-150 degrees from the cut portion 12. Short shot due tosuch a displacement of the gate can be removed by adjusting theinjection pressure and injection speed of the molding material. In thecase where the flow length is too long or the flow lengths are extremelyunbalanced, it sometimes occurs that the molding material is not filledfully into the die even if the injection pressure and injection speedare changed. Therefore, it is preferred that the gate 3 is located sothat the flow lengths become balanced as much as possible. When thediameter of the cavity is 52-65 mm, for example, it is preferred thatthe gate 3 is set at an angle of approximately 90-135 degrees from themold cut portion 12.

The structure in the vicinity of the cut portion 2 in FIG. 7 isvirtually the same as that shown in FIG. 4B.

In the forming die 4F shown in FIG. 7, no cut portion is provided in theforming die 4F. Hence, there is no need of considering the balancing ofthe flow lengths. The two flows of the molten material divided into twodirections through the circular cavity 4f at the gate 3 meet each othervirtually at the position opposing the gate 3. The weld portion 14 isformed at the meeting position. The diameter of the cavity 4f isapproximately 52 mm and the gate 3 is positioned at an angle ofapproximately 135 degrees from the cut portion 2. The position of thegate 3 is set so that not only the gate 3 is apart from the oppositeportion 15 to the cut portion 2 but also the weld portion 14 is formedat a portion apart from the opposite portion 15 to the cut portion 2.When the diameter of the cavity 4f is 52-65 mm, for example, it ispreferred that the position of the gate 3 is set at an angle ofapproximately 90-135 degrees from the cut portion 2.

In the case where molding is performed with the use of such a formingdies with a previously formed cut portion 12 as the forming die 4D ofFIG. 5 and the forming die 4E of FIG. 6, two flows of the moldingmaterial injected from the gate 3 will not meet each other and, hence,no weld portion is produced.

A method for setting a preferred gate position in molding a seal ringwith the use of the forming die 4E shown in FIG. 6 will be describedconcretely.

FIG. 8A and FIG. 8B show an example of a seal ring 6 being 52 mm inouter diameter, 2.3 mm in width, and 2.45 mm in thickness. Experimentswere conducted on the seal ring 6 shown in FIG. 8A and FIG. 8B with thegate position in the molding die 4E of FIG. 6 changed in various ways.When the position of the gate 3 relative to the mold cut portion 12 waschanged to 90 degrees, 135 degrees, and 180 degrees, the allowableextended length L of the mold cut portion (FIG. 9) varied as shown inthe graph of FIG. 10.

According to the graph of FIG. 10, although no sharp changes in theallowable extended length L of the mold cut portion 12 are observed, itis known that the allowable extended length L of the mold cut portion 12obtained when the gate 3 is placed away from the opposite portion 15 tothe cut portion 12 is larger than that obtained when the gate 3 isplaced at the opposite portion to the cut portion (at 180 degreestherefrom) and the strength is correspondingly improved.

In this case, if the gate 3 is placed too much away from the oppositeportion 15 to the cut portion 12, the flow lengths become unbalanced andshort shot becomes liable to occur. Therefore, it is preferred that thegate 3 is set at a position forming an angle of approximately 135degrees with the cut portion 12.

Also when a seal ring is formed by the use of the forming die 4F of FIG.7, widening of the cut portion 2 of the seal ring 6 produces stressconcentration at the opposite portion 7 to the cut portion 2. Therefore,the position of the gate 3 is set according to the above describedmethod.

Also when a seal ring 6 has a larger outer diameter, a seal ringimproved in strength and loadability can be produced by similarlysetting the gate 3 at other portion than the opposite portion 15 to thecut portion 2.

EXAMPLE 2

Example 2 of the invention is an example in which a seal ring is moldedout of a PFA-based molding material.

PFA has a high melting point and is softer than PEEK However, PFA is aresin having fragility due to weak molecular bond. Therefore, if thegate is set at the portion opposite to the cut portion, a seal ringformed of the PFA-based molding material is liable to break at theopposite portion to the cut portion when the cut portion is widened.

In the case of Example 2, the gate is provided at a portion other thanthe opposite portion to the cut portion.

Since the seal ring molding formed of the PFA-based material is soft itis possible to make a cut therein with a knife after it has been molded.

Seal ring moldings formed of the PFA-base material can be molded byinjecting the molten material into the cavity 4e of a forming die 4Ehaving a mold cut portion 12 as shown in FIG. 6.

It is also possible to produce seal ring products formed of thePFA-based material by forming the seal ring by the use of a forming die4G joined at the mold cut portion 12 (or having no cut portion) as shownin FIG. 11 and, after the forming, by cutting the mold cut portion 2 atthe position indicated by the broken line.

In the case where the seal ring is molded by the use of the forming die4G of FIG. 11, a weld portion 14 is formed in the seal ring at theposition virtually opposing the gate 3. The weld portion 14, as well asthe portion-corresponding-to-gate 13, has inferior strength as comparedwith other portions, and therefore, the position of the gate 3 is setsuch that the weld portion 14 and the portion-corresponding-to-gate 13are located at positions other than the opposite portion 15 to the cutportion 2.

A method for setting the gate position in the manufacture of a seal ring7 being 65 mm in outer diameter, 2.3 mm in width, and 2.3 mm inthickness as shown in FIG. 12A and FIG. 12B will be described.

Experiments were conducted on the seal ring 7 shown in FIG. 12A and FIG.12B with the gate position 3 of the forming die 4G shown in FIG. 11changed in various ways. When the position of theportion-corresponding-to-gate 13 relative to the cut portion 2 of theseal ring 7 is changed, the allowable extended length L of the cutportion 2 (FIG. 5) of the seal ring 7 exhibited variations as shown inthe graph of FIG. 13.

In this case, since the forming die 4G used has no cut portion, theproblem of unbalanced flow lengths does not occur. However, the flowlength becomes greater according as the outer diameter becomes larger,and therefore, it is preferable to adjust the injection pressure andinjection speed of the molding material to avoid the trouble of shortshot

Referring to the graph of FIG. 13, it is known that the allowableextended length of the cut portion 2 is the largest when the gate 3 ofthe forming die 4G is provided at a position 90 degrees apart from thecut portion 2. The allowable extended length of the cut portion 2becomes the smallest when the gate 3 is provided at a position of theopposite portion 15 to the cut portion 2, namely, at a position 180degrees apart from the cut portion 2. Since the weld portion 14 isformed at a position virtually opposing the position of the gate 3, theweld portion 14 comes to be produced closer to the opposite portion 15to the cut portion 2 as the angle formed between the cut portion 2 andthe gate 3 becomes smaller than 90 degrees. As a result, a strengthsimilar to that obtained when the portion-corresponding-to-gate 13 isset closer to the opposite portion 15 to the cut portion 2 is obtained.

Accordingly, in this case, the strength becomes the highest when theportion-corresponding-to-gate 13 is set in a position 90 degrees apartfrom the cut portion 2. Hence, it is preferable to set theportion-corresponding-to-gate 13 at this position. Thus, the strength ofthe seal ring is improved by setting the position of the gate 3 suchthat the portion-corresponding-to-gate 13 and the weld portion 16 areformed at positions other than the opposite portion 15 to the cutportion 2. Further, the breakage of the opposite portion 15 to the cutportion 2 occurring when the seal ring is loaded in place can beprevented and its loadability can be improved.

Variations

While an example for a PEEK-based material and an example for aPFA-based material were described above, the invention is not limited tothese.

The range in which the gate 3 should be provided for the forming diedepends on the flow length, flow passage area, and viscosity of thematerial. Even when a different shape from the above is produced or adifferent material from the above is used, the strength and loadabilityof the seal ring can be improved by providing the gate 3 at a positionother than the opposite portion 15 to the cut portion 2 afterinvestigation of the shape and material

The shape of the cut portion 2 is not limited to those mentioned in theExamples 1 and 2. A bias cut, a stepped cut, and the like are alsopossible.

What is claimed is:
 1. A method for manufacturing a seal ring,comprising the steps of:injecting a single material from a gate of aforming die into a circular cavity of said die in two directions so thatsaid ring is made of two flows of said single material in such a waythat a common flow start portion of said two flows is located at saidgate where said two flows start, and forming a cut portion at oneposition on a circumference of said ring, wherein said flow startportion is located at a position spaced apart at an angular displacementalong the circumference from an opposite portion to said cut portion,said opposite portion being at 180 degrees from said cut portion, acrossthe diameter of said ring, wherein said flow start portion is positionedat an angle of approximately 90 to approximately 135 degrees from saidcut portion.
 2. The method as defined in claim 1, wherein the injectingstep includes forming a weld portion at a position where said two flowsof said single material meet each other.
 3. The method as defined inclaim 2, wherein the step of forming said cut portion includes cuttingsaid ring at a position spaced from-said weld portion so as to form saidcut portion.
 4. The method as defined in claim 1, wherein during theinjecting step, said cut portion is formed between two front ends ofsaid two flows of said single material within said circular cavity ofsaid die.